Field of the Invention
The invention lies in the integrated technology field. More specifically, the invention relates to an integrated memory having memory cells, arranged at crossover points of word lines and bit lines, and reference cells, arranged at crossover points of a reference word line and the bit lines and serve for generating a reference potential on the bit lines prior to a readout of the memory cells.
Such an integrated memory in the form of a ferroelectric memory or FRAM (Ferroelectric Random Access Memory) is described in U.S. Pat. No. 5,844,832. Prior to a read access to the memory cells, a specific potential is written to the reference cells and the latter are subsequently read out onto the bit lines. Afterwards, in each case two adjacent bit lines onto which reference cells having different levels were read out are short-circuited with one another, so that a reference potential corresponding to the average value of the two different levels is established on these two bit lines. The reference cells are thereby constructed identically to the regular memory cells. Prior to each readout of the memory cells, that is to say, for example, also during a test of the memory cells, the reference potential is generated on the bit lines by means of the reference cells in the manner described in order to feed the defined reference potential to sense amplifiers, which are connected to the bit lines, prior to an evaluation of the bit line potentials which is to be carried out by the sense amplifiers.
Errors during the readout of one of the memory cells in the prior art memory can have two different causes. On the one hand, the memory cell that is currently to be read out or the word line connected to it may have a defect. On the other hand, the associated reference cell may have a defect, so that the reference potential is not generated correctly, thereby preventing error-free evaluation of the bit line potential by the sense amplifiers. It is desirable, therefore, to be able to ascertain whether or not an error occurring during the readout of one of the memory cells is caused by a malfunction of the reference cells.